org.azyva.dragom.execcontext.plugin

Interface ToolLifeCycleExecContextPlugin

public interface ToolLifeCycleExecContextPlugin

Implemented by ExecContextPlugin implementations that need to be informed of tool life cycle.

This allows an ExecContextPlugin to explicitly bind itself to an ExecContext information scope.

The ExecContext implementation having an ExecContextPlugin whose implementation implements this ToolLifeCycleExecContextPlugin is expected to behave in the following manner:

• If isTransient() returns true, it must create and release the ExecContextPlugin for each tool execution. This implies that the ExecContextPlugin is bound to tool scope;
• If isTransient() returns false, it can keep the ExecContextPlugin instance alive in between tool execution. This implies that the ExecContextPlugin is bound to workspace scope;
• It should call startTool() during tool initialization;
• It should call endTool() during tool termination.

An ExecContext implementation is not forced to handle ToolLifeCycleExecContextPlugin. In such a case, it must treat the ExecContextPlugin as if isTransient returns true, implying tool binding. If isTransient actually returns false, the fact that the ExecContextPlugin is anyways released after each tool execution should not do any harm apart from reduced performance due to not reusing instances when a single JVM is used for multiple tool executions. That is why it is not guaranteed that startTool and endTool will be called. But if they are not, instances will necessarily not be reused across tool executions.

If an ExecContextPlugin implementation does not implement that interface and the ExecContext implementation does handle it, it must treat the ExecContextPlugin as if isTransient returns false, implying workspace binding.

The two above paragraphs may seem incoherent (assume isTransient returns true in one case and itTransient returns false in the other). But they are not. The idea is that if an ExecContextPlugin does not implement that interface, it implicitly "agrees" to be bound to workspace scope, the default. But if the ExecContextPlugin does implement this interface and isTransient returns true, it effectively does not support workspace scope, whereas all ExecContextPlugin's implicitly support tool scope, even if isTransient returns false.

If isTransient returns false and ExecContextPlugin's instances are reused across tool executions, it also implies that two tools could execute simultaneously on the same ExecContext (on different threads), and thus with the same ExecContextPlugin instance. It is up to the ExecContextPlugin to handle this situation, or prevent it from happening. DefaultWorkspacePluginFactory from dragom-core prevents this from happening by locking the workspace directory, and thus the ExecContext to which it is associated, using a marker lock file.

Author:

David Raymond

Method Summary

Modifier and Type	Method and Description
void	endTool() Informs the ExecContextPlugin that a tool is terminated with the ExecContext holding it.
boolean	isTransient()
void	startTool() Informs the ExecContextPlugin that a tool is started with the ExecContext holding it.

Method Detail

isTransient

boolean isTransient()

Returns:

Indicates that the ExecContextPlugin must not be reused across tool executions, implying tool binding. If false, the ExecContextPlugin may be reused across tool executions, implying workspace binding.

startTool

void startTool()

Informs the ExecContextPlugin that a tool is started with the ExecContext holding it.

This gives an opportunity to the ExecContextPlugin to perform per-tool initialization.

endTool

void endTool()

Informs the ExecContextPlugin that a tool is terminated with the ExecContext holding it.

This gives an opportunity to the ExecContextPlugin to perform per-tool cleanup.